Certain immersion objective lenses for microscopes that enable an operator to correct aberrations resulting from changing optical characteristics of the specimen chamber are known from the prior art. These aberrations include spherical aberration, for example, which occurs as a result of variations in the density of the immersion fluid used or inhomogeneities in the biological structure of the specimen to be observed. Particularly in the case of objective lenses having a high numerical aperture, at a large working distance and with large refractive index contrasts in the beam path between objective lens and specimen, substantial spherical aberration often occurs.
U.S. Pat. No. 8,705,178 B2 discloses an objective lens for a microscope that comprises a first lens group having positive refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power and a fourth lens group having positive refractive power that are arranged in this sequence from an object side. The second lens group constitutes a correction member that can be moved along an optical axis in order to correct the spherical aberration. The second lens group has a refractive power that is approximately equal to or greater than the total refractive power of the objective lens. However, this objective lens is not suitable for use as an immersion objective lens.
Another objective lens that also has only one correction member that can be moved along the optical axis is known from U.S. Pat. No. 5,940,220. Compared to the previously mentioned objective lens, the refractive power of the correction member that can be moved along the optical axis is small in relation to the total refractive power of the objective lens. A corrective effect results from the position of the correction member within a divergent or convergent beam path, which can be varied by moving the correction member. The relatively low refractive power of the correction member has the disadvantage that the objective lens must have a long overall length in order to achieve a great corrective effect, and the diameter of the objective lens increases with the overall length, which is disadvantageous in many microscopy applications.
Finally, an immersion objective lens is known from DE 10 2004 051 357 A1 in which a plurality of lens groups are moved in order to correct spherical aberration. This construction is characterized by a high level of mechanical complexity, which is associated with high production costs and frequent need for repairs.